Amplitude-versus-offset (AVO) procedures commonly used today are made up essentially of three steps. The first step is the estimation of two parameters, usually either the intercept and gradient terms, or scaled versions of compressional and shear reflectivity. The second step is the measurement of the general temporal and spatial variation of the relationship between these two parameters. This slowly varying relationship we call the background trend. The final step is the display of the data with this background trend removed. This display we call the Fluid Factor. It aims to produce interpreter sections whose amplitude is close to zero everywhere, except at the top and base of hydrocarbon bearing zones.